1. Field of the Invention
This invention relates generally to methods and compositions for consolidating solids, and more particularly, to improved methods and compositions for consolidating existing or placed solids in subterranean zones penetrated by well bores.
2. Description of the Prior Art
Various sand consolidation and gravel packing methods and techniques have been developed and employed heretofore for preventing or inhibiting the migration of loose sands and the like with fluids produced from subterranean formations. A particularly successful method of achieving control of such solids involves placing a hardenable consolidating fluid into a subterranean formation whereby the consolidating fluid coats solids existing therein or placed in the formation with the consolidating fluid, and thereafter, causing the consolidating fluid to harden whereby the solids are consolidated into a hard permeable mass. The hard permeable mass allows fluids to be produced from the subterranean formation, but loose sands and the like are prevented from migrating with the produced fluids.
Gravel packing methods and techniques utilized heretofore have generally included placing a solids consolidating fluid and solids coated therewith into a subterranean zone using a thickened aqueous or hydrocarbon base carrier fluid of relatively high viscosity. While such high viscosity carrier fluids can carry high concentrations of solids therewith, they suffer from the disadvantage that rapid dissipation of the carrier fluids into surrounding formations does not occur during the placement of solids. This often results in voids being formed in the solids pack produced. In addition, such high viscosity carrier fluids can cause damage to the permeability of formations into which they are caused to flow. Thus, in gravel packing and other similar procedures employed in subterranean zones, there is a need for a method whereby a carrier fluid of low viscosity can be utilized to place consolidating fluid coated solids into the zones. The low viscosity carrier fluid will rapidly be lost to formations surrounding the zones resulting in the packing of solids at greater velocities and high solids-low carrier fluid masses being produced in the pack zones.
Other disadvantages of carrying out subterranean zone treatments using thickened carrier fluids such as aqueous gels is that such thickened fluids usually require considerable surface preparation equipment and mixing time and often significantly lose viscosity by heat and shear as the fluids are pumped through the well bore into a subterranean zone. The loss in viscosity can and often does result in improper placement of solids and/or other undesirable results.
Consolidating methods utilized heretofore for consolidating solids existing in or placed into subterranean zones have heretofore required several steps to carry out. For example, methods for placing and consolidating solids in subterranean zones have often involved the steps of first placing consolidating fluid-coated solids in the zones followed by contacting the coated solids with overflush fluids containing catalyst. Further, the consolidating fluids heretofore utilized have been difficult to use at low temperatures, e.g., at temperatures less than about 100.degree. F. That is, when the zone in which the consolidating fluid is utilized has a temperature such that the temperature of the consolidating fluid is below about 100.degree. F., long cure times of the consolidating fluid and the use of high quantities of catalyst are often involved. Thus, there is a need for a consolidating fluid-low viscosity carrier fluid composition and method of using such composition whereby the consolidating fluid-carrier fluid composition, the solids to be placed and consolidated thereby and the catalyst used can be combined on-the-fly if desired; whereby solids can be efficiently consolidated at temperatures below about 100.degree. F.; and whereby because of the low viscosity of the carrier fluid and resultant rapid dissipation thereof into subterranean formations, minimum damage to the formations occurs and the occurrence of unpacked regions in gravel packs produced is minimized. The term "on-the-fly" is used herein to mean continuous mixing of components as the resulting mixture is pumped into a well bore and subterranean zone penetrated thereby. By the present invention, methods and compositions for consolidating existing or placed solids in subterranean zones meeting the needs recited above are provided.